Anhedonia-diminished pleasure from normally rewarding activities-is a cardinal feature of Major Depressive Disorder (MDD) and other disorders involving the broader RDoC Positive Valence Systems domain. Recent research has emphasized how motivational factors, such as the processing and weighting of rewards and incentives, underlie depressive anhedonia. A problem, however, is that most studies use single-shot tasks that hold critical factors constant or combine distinct factors. This AREA R15 translates motivational intensity theory-a successful basic-science theory of biobehavioral effort regulation-to illuminate depressive anhedonia. Because of its extensive empirical support and established research paradigms, motivational intensity theory enables researchers to diagnose whether MDD's motivational deficits are rooted in (1) diminished incentive value (finding goals less rewarding), (2) higher perceptions of task difficulty (seeing tasks as too hard, or (3) both. The proposed research will recruit a sample of 50 community adults: half will meet DSM-V criteria for primary MDD, and half will be healthy matched controls. Participants will first complete laboratory tasks that isolate and manipulate key factors (incentive value, task difficulty) and measure effort engagement using cardiac autonomic activity, particularly sympathetic nervous system activity, by means of impedance cardiography. Participants will then take part in an innovative one-day ecological momentary assessment that combines traditional self-reported experience sampling with ambulatory impedance cardiography. This day-long assessment will offer the first look at cardiac markers of effort engagement in the daily lives of people with MDD as they engage with their everyday goals and challenges, and it will allow an evaluation of the generality of cardiac autonomic effort deficits from the lab to daily lie. The project thus introduces several significant innovations: (1) it translates a prominent theory o effort to illuminate the motivational substrates of anhedonia in MDD, using incisive biological measures; (2) it combines ambulatory impedance cardiography, a cutting-edge method, and traditional experience sampling to characterize MDD's motivational deficits in daily life; and (3) t evaluates the generality of MDD's motivational deficits across laboratory and everyday contexts. Finally, as an R15 AREA proposal, this research offers a unique opportunity for undergraduate students to get involved in translational clinical research that applies innovative biological methods to a profound public health problem.